Magnetic fingerprint dusting brushes have been used for some time by various police forces in the process of dusting for fingerprints at the scene of a crime.
A known brush has a handle similar to the handle of a conventional artist's brush but carrying a small cylindrical permanent magnet instead of bristles. In use, the magnet is dipped into a jar of ferrous powder which is mixed with a quantity of powdered carbon or the like dusting powder. The ferrous powder clings to the magnet along the lines of force of the magnetic field and forms a bristle-like array which serves as a carrier for the dusting powder. The magnetic brush is then used in place of a conventional brush to locate and identify latent fingerprints, the dusting powder transferring from the aligned ferrous powder particles to the print area.
In the known art, the loading of a `magnetic brush` and the subsequent unloading after use can be a messy procedure. Some prior art magnetic brushes have a retractable magnet within a non-ferrous blind sleeve, so that when the magnet is retracted the ferrous powder is intended to be forced to drop off, for example into a storage jar. However, a residue of carbon powder often remains on the sleeve, so that it still has to be cleaned properly before it can be stored, as for example in the user's pocket.